Bond strength-coordination number fluctuations and the fragility of some ion-conducting oxide and chalcogenide glass-forming liquids

Abstract

The concept of fragility has been used widely to characterize the temperature dependence of the viscosity of glass-forming liquids. According to a model proposed by one of the authors, the fragility is determined by the relaxation of structural units that form the melt and is described in terms of the bond strength, coordination number, and their fluctuations. In the present contribution, the model is applied to investigate the temperature dependence of the viscosity of some ionconducting oxide and chalcogenide glass-forming liquids. From the analysis of the model, physical quantities such as the number of bonds that must be broken to observe the viscous flow are obtained. The analysis suggests also that good ionic conductors have an intermediate value of fragility.

A comparative study of the viscosity of ion conducting polymers based on the bond strength-coordination number fluctuation model and other models

“…2. The relation follows a trend suggested in previous studies [5]. That is, B decreases with the increase of C. In the figure, theoretical curves based on the BSCNF model are shown for different values of δ0ln (η Tg /η 0 ).…”

“…It has been applied in oxides, semiconducting chalcogenides, metallic, and some polymeric systems [5]. In this model, the melt is considered to be formed by an agglomeration of structural units.…”

“…This means that for the materials in consideration, the viscosities at T g and at the high temperature limit T 0 are different from the usual values η Tg 010 12 Pa·s and η 0 010 −5 Pa·s, respectively. The usual value adopted in the Angell's plot is δ039.1 [5].…”

“…However, fundamental understanding of the physical properties of the materials is not sufficient. For instance, previous study has indicated that the optimization of the ionic conductivity could be searched by studying the viscosity-conductivity relation [5,6]. However, its physical background was not clear.…”

“…The result indicated that the viscosity of the system is controlled by the connectivity of the structural units of trehalose molecules. It has been also shown that good ionic conductors have intermediate values of fragility [5].…”